🔩 Absorbed energy of metals — Charpy impact test (V-notch and U-notch test pieces, pendulum impact tester)
In short
A test piece 55 mm × 10 mm × 10 mm with a V-notch (45°, depth 2 mm, root radius 0. The test is performed according to PN-EN ISO 148-1:2017-02 + Ap1:2025-12; Standard test piece: Length 55 mm, square cross-section with a side of 10 mm, notch at mid-length. The procedure comprises 8 steps; it is used for: Acceptance of structural steels and steel products (absorbed energy KV at a specified temperature), Determination of the ductile-to-brittle transition temperature from a series of tests at different temperatures, Testing of welded joints: test pieces from the parent metal, the weld and the heat-affected zone.
At a glance
- Standard: PN-EN ISO 148-1:2017-02 + Ap1:2025-12
- Category: Materials and NDT
- Procedure steps: 8
- Standard test piece: Length 55 mm, square cross-section with a side of 10 mm, notch at mid-length
- V-notch: Included angle 45°, depth 2 mm, root radius 0.25 mm
- U-notch: Root radius 1 mm (unless otherwise specified)
Overview
The standard specifies the method for the Charpy impact test (V-notch and U-notch) for determining the energy absorbed in breaking metallic test pieces; it does not cover instrumented tests, which are described in ISO 14556. The test consists in breaking a notched test piece with a single blow of a pendulum; the notch has a specified geometry and lies in the middle between two supports, on the side opposite to the point of impact.
Because the impact toughness of many metallic materials depends on temperature, tests are carried out at a specified temperature; at a temperature other than ambient the test piece is heated or cooled under controlled conditions. The Charpy test is often used as a routine high-throughput "pass/fail" acceptance test; in research and design work, on the other hand, the energy values are analysed, together with whether the test piece was completely broken, partially broken or only plastically deformed. Results obtained with testers with different striker radii and on test pieces of different shapes are not directly comparable — therefore, apart from compliance with ISO 148, full reporting of the type of tester, the test piece and the condition of the test pieces after the test is essential.
The Regional Office of Measures in Łódź, accredited by PCA for the calibration of Charpy pendulum testers, describes the "direct" method of verification: the absorbed energy is calculated as the difference in the potential energy of the pendulum between the initial position (angle α, usually 150°–160°) and the final position (angle β) using the formula K = Fg · l · (cos β − cos α), where Fg is the gravitational force of the pendulum and l is the pendulum length; the most commonly used testers have a nominal energy of 300 J.
CONTENT OF AMENDMENT Ap1:2025-12 READ (22.09.2026). Three changes, all in Annex E (informative, on uncertainty): the symbol uKV changed to νKV in formula E.6, a grammatical correction in Table E.2 and the symbol u(KV) changed to U(KV) in Table E.3. None of them affects the test requirements or the result — of the Ap amendments described in this database, this is the only purely editorial change.
Method principle
The notched test piece lies freely on two supports, resting against the anvils, so that the plane of symmetry of the notch is within 0.5 mm of the mid-plane between the anvils. The released pendulum strikes with its striker in the plane of symmetry of the notch, on the side opposite to the notch, and breaks the test piece with a single blow. Part of the pendulum energy is absorbed by the test piece, and the rest raises the pendulum to the angle β, which is a measure of the resistance of the test piece to impact — the smaller the angle, the more energy the test piece absorbed. The result is read from the dial of the tester, graduated in degrees or directly in units of energy, and corrected for friction losses. The energy is designated KV or KU, with the subscript 2 or 8 indicating the striker radius (e.g. KV2). Besides the absorbed energy, the lateral expansion and the percentage of shear fracture are usually determined.
Applications
- Acceptance of structural steels and steel products (absorbed energy KV at a specified temperature)
- Determination of the ductile-to-brittle transition temperature from a series of tests at different temperatures
- Testing of welded joints: test pieces from the parent metal, the weld and the heat-affected zone
- Assessment of the effects of heat treatment and ageing of the material
- Calibration and verification of pendulum testers by the direct method (offices of measures, calibration laboratories)
Key parameters
| Parameter | Value |
|---|---|
| Standard test piece | Length 55 mm, square cross-section with a side of 10 mm, notch at mid-length |
| V-notch | Included angle 45°, depth 2 mm, root radius 0.25 mm |
| U-notch | Root radius 1 mm (unless otherwise specified) |
| Reduced-section test pieces | Thickness 7.5 mm, 5 mm or 2.5 mm, when a standard test piece cannot be taken |
| Pendulum striker | Radius 2 mm or 8 mm — recorded as a subscript (KV2, KV8, KU2, KU8); results for the two strikers may differ |
| Nominal energy of the tester | Value stated by the manufacturer; the most commonly used testers have 300 J (data of the Regional Office of Measures in Łódź) |
Standard
- Standard number
- PN-EN ISO 148-1:2017-02 + Ap1:2025-12
- Title (PL)
- Metale — Próba udarności sposobem Charpy'ego — Część 1: Metoda badania
- Title (EN)
- Metallic materials — Charpy pendulum impact test — Part 1: Test method
Step-by-step procedure
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Preparation of test pieces
Make test pieces 55 mm long with a 10 mm × 10 mm cross-section and a V-notch or U-notch; if a standard test piece cannot be taken, use a reduced-section test piece (7.5 / 5 / 2.5 mm). Machine the notch carefully so that the root is free of machining marks; the plane of symmetry of the notch perpendicular to the longitudinal axis of the test piece. Heat-treated materials: finish machining and notching after the final heat treatment.
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Marking
The test piece may be marked on a surface not in contact with the supports, anvils or striker, at a location where the deformation and discontinuities caused by marking will not affect the absorbed energy.
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Friction check
Every day before the first test check the energy absorbed by friction: release the tester without a test piece and read the angle of rise β1 (or K1), then, without resetting the pointer, carry out a second swing and read β2 (K2); the pointer friction loss p = M(cos β1 − cos β2) or p = K1 − K2.
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Bearing and air resistance losses
After determining β2 return the pendulum to the initial position and, without resetting the pointer, release it, allowing it to make 10 half-swings; after the 11th begins, move the pointer to approx. 5 % of the range and record β3 (K3). Losses per half-swing: p′ = 1/10 · M(cos β3 − cos β2).
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Test temperature
Carry out the test at the specified temperature; at a temperature other than ambient heat or cool the test piece under controlled conditions.
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Positioning the test piece
Place the test piece squarely on the anvils, with the plane of symmetry of the notch within 0.5 mm of the mid-plane between the anvils, and the notch on the side opposite to the blow.
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Impact and reading
Release the pendulum and break the test piece with a single blow; read the absorbed energy from the dial (or calculate it from the angle of rise), taking into account the correction for friction. Designate the result KV2, KV8, KU2 or KU8.
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Fracture assessment and report
Usually also determine the lateral expansion and the percentage of shear fracture; describe the condition of the test pieces after the test (completely broken, partially broken, deformed) and the type of tester and test piece — without this the results are not comparable between laboratories.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Charpy pendulum impact tester | Installed and verified in accordance with ISO 148-2; dial graduated in degrees or in units of energy | — |
| Pendulum striker | With a radius of 2 mm or 8 mm, according to the product specification | — |
| Supports and anvils | Fixing the position of the test piece; centring shims are used with reduced-section test pieces | — |
| Device for heating or cooling test pieces | For tests at a temperature other than ambient, with control of conditions | — |
| Measuring instruments for test pieces | For checking the dimensions of the test piece and the notch; measurements with metrological traceability | — |
| Calibration equipment | Measurement of the gravitational force of the pendulum, the pendulum length and the angles α and β — direct method according to the Regional Office of Measures | — |
Health and safety (OHS)
- Pendulum with energy up to 300 J — workstation guards closed, swing zone free of people, pendulum locked when inserting the test piece
- Fragments of the test piece ejected at high speed — guard and safety glasses
- Cooled (e.g. in a cooling liquid) and heated test pieces — thermal gloves, tongs for handling
- Sharp edges of the notch and fragments — gloves when collecting test pieces after the test
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 148-1:2017-02 + Ap1:2025-12 — “Metallic materials — Charpy pendulum impact test — Part 1: Test method”.
How does this method work?
The notched test piece lies freely on two supports, resting against the anvils, so that the plane of symmetry of the notch is within 0.5 mm of the mid-plane between the anvils.
What is the measuring range and accuracy?
Standard test piece: Length 55 mm, square cross-section with a side of 10 mm, notch at mid-length; V-notch: Included angle 45°, depth 2 mm, root radius 0.25 mm; U-notch: Root radius 1 mm (unless otherwise specified); Reduced-section test pieces: Thickness 7.5 mm, 5 mm or 2.5 mm, when a standard test piece cannot be taken.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Charpy pendulum impact tester, Pendulum striker, Supports and anvils, Device for heating or cooling test pieces, Measuring instruments for test pieces, Calibration equipment.
Where is this test used?
Acceptance of structural steels and steel products (absorbed energy KV at a specified temperature); Determination of the ductile-to-brittle transition temperature from a series of tests at different temperatures; Testing of welded joints: test pieces from the parent metal, the weld and the heat-affected zone; Assessment of the effects of heat treatment and ageing of the material; Calibration and verification of pendulum testers by the direct method (offices of measures, calibration laboratories).
What safety precautions apply?
Pendulum with energy up to 300 J — workstation guards closed, swing zone free of people, pendulum locked when inserting the test piece; Fragments of the test piece ejected at high speed — guard and safety glasses; Cooled (e.g. in a cooling liquid) and heated test pieces — thermal gloves, tongs for handling; Sharp edges of the notch and fragments — gloves when collecting test pieces after the test.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 148-1.